The average weight of 12 articles is 18 kg. Addition of another new article reduces the average weight by 500g. What is the weight of the new article?

11.5 kg

Sum of weight of 12 articles = 12 × 18 = 216 kg

By adding 1 new article , New average = 17.5 kg

Sum of weight of 13 articles = 13 × 17.5 = 227.5 kg

Weight of new article = 227.5 - 216 = 11.5 kg